what's going to happen tonight, because, as david pointed out, this format is so loose. once they get into the discussion, almost anything can happen. they could directly challenge each other. jim lehrer could directly challenge them. but they really don't know. >> it is going to be such an exciting night. and a reminder that george and i will be right here with you and the abc news team, ready to react and analyze and fact check. one-on-one, the candidates debate, 9:00 p.m. eastern, 6:00 central. and we move on now on "world news" because we have two developing stories from overseas. tonight in syria, the city of aleppo, their new york city, four car bombs killed nearly 40 people. eyewitnesses describe what felt like a series of earthquakes, giant buildings flattened. and here, a square before and after, you can see there, reduced to rubble. and, in iran, something we rarely see. clashes in the streets of tehran, as hundreds of protesters take on their own government.